So my 3GS will be coming in the mail tomorrow (can't wait, bought for $125), and I need to use it on Tmobile. It's currently running something in the 3's as I can see the bright gray dock background in the pictures of it. I'm going to update via pwnagetool, legally activate it with an unused ATT sim in iTunes (that will work right?) but I'm lost from there.

I don't have a data plan, I'm on T-Mobiles new $15 a month prepaid SMS/MMS plan, and 10 cents a minute. What do i need to do to get SMS and MMS (and phone calls) working on Tmobile?